This proposal is directed toward the mechanism(s) of thromboembolic complications caused by biologic agents, such as disseminated intravascular coagulation, which contributes to the mortality of patients with sepsis due to endotoxin-producing bacteria, and to patients with staphylococcal infections such as Toxic Shock Syndrome. We plan to investigate the cellular and molecular pathology of endotoxin's action toward human target cells includeing platelets and endothelial cells. Since Lipid A is responsible for the interaction of endotoxin with human platelets, we plan to focus our effort on determining the molecular basis for Lipid A action on the cell membrane of human cells. We will use isotope tracer, immunological and enzymatic analysis to determine the binding of Lipid A to platelets and endothelial cells, and functional changes in their membranes. We will investigate the mechanism of action of staphylococcal products on the blood clotting system with emphasis on changes in the Fc receptor on human platelets induced by Protein A-Fc fragment complex. Also, an experimental model of intravascular coagulation following injection of staphylocci will be established to assess the role of Protein A and other toxic products in vivo in triggering intravascular coagulation and shock syndrome. Finally, we will continue our research on the problem of the interaction of staphylococci with fibrinogen, which we developed as the staphylococcal clumping test for measurement of fibrinogen and fibrin degradation products. Staphylococcal cell wall receptor for fibrinogen (clumping factor) will be isolated, purified, and characterized. The molecular mechanism of binding of fibrinogen to the staphylococcal cell wall receptor will be investigated. The results of the proposed research should generate fundamental information on the molecular mechanism of the toxic effect of gram negative bacteria and staphylococci on human cells and proteins involved in triggering blood clotting and bring about the development of new methodological approaches to measure these interactions.